People running sites with user generated content (forums, comments etc.) can check they're not unknowlingly linking to dodgy neighbourhoods/spam. You can keep an eye on your IBL to Outgoing ratio.
linkvendor.com/seo-tools/outbound-links.html check this tool. i use this and soon i will publish my advanced inbound and outbound link shower. Regards, Mustafa
check out your own outgoing ones, as TOPS30 mentioned. you can also see who your competition (or someone doing very well) is linking to... decent way to at least get a start to finding out what other sites may be owned by them, though obviously it'd just be getting you started; more research would be needed.